The present invention relates to baseball or softball bats. More particularly, the present invention relates to a baseball or softball bat capable of increasing the hit distance of a ball and reducing the manufacturing cost.
Conventionally, the baseball or softball bat (hereinafter, referred to as a bat) market deals with bats of various materials. For example, there are wooden bats, metal bats made of titanium alloys or aluminum alloys, and fiber reinforced plastic (hereinafter, referred to as FRP) bats which are manufactured by impregnating a matrix resin, represented by an epoxy resin and other synthetic resins, into yarns, cloths, Sleeves or the like, which are formed of carbon fibers, glass fibers or the like, and curing the impregnated yarns, doths, sleeves or the like.
In order to improve the rebound characteristics of a bat when it hits a ball, Japanese Patent Publication No. 50-7976, for example, previously proposed a metal bat with a double pipe structured hitting surface which is formed by bonding a metal pipe of a suitable length inside the hitting surface of the bat body.
Japanese Utility Model Publication No. 51-13165 also proposed a metal bat with a triple structured hitting surface which is formed by bonding a metal pipe of a suitable length inside the hitting surface of the bat body, and then inserting and adhering a lubber or synthetic resin plate or pipe in the interlayer of double pipes, which are formed of the bat body and the bonded metal pipe, (in the layer between the bat body and the bonded metal pipe).
U.S. Pat. No. 5,415,398 also proposed a bat which has a tubular insert placed and bonded inside the hitting portion of the bat body so as to leave a gap between the insert and the bat body, or a bat which contains grease sealed in the gap.
However, the conventionally proposed bats as described above have the following problems.
As described above, the bat disclosed in Japanese Patent Publication No. 50-7976 has a metal pipe of a suitable length bonded inside the hitting surface of the bat body. In manufacturing such a bat, a metal pipe is inserted and bonded in the hitting surface of the bat body while the pipe is under heavy load or pressure. In the process of inserting and bonding the metal pipe, the inner wall of the hitting surface of the bat body may be damaged. If the inner wall of the hitting surface is thus damaged, the bat may crack from the damaged portion or may be broken in use.
The bat disclosed in Japanese Utility Model Publication No. 51-1316 has a rubber or synthetic resin plate placed in the interlayer of double pipes as described above. That causes a dull sound and reduces the rebound characteristics of the bat when the bat hits a ball.
A bat body deforms more as the bat hitting portion is thinner. The bat can hit a ball farther by utilizing the force of restoring the bat body from the deformed shape to the original shape. When the bat body hitting portion is too thin, however, the strength of the bat body is insufficient. Therefore, the bat body may dent or crack when hitting a ball.
In order to solve such problems, the bat disclosed in U.S. Pat. No. 5,415,398 has the above described structure to prevent the outer shell wall of the thin bat body from being plastically deformed by impact stress caused when the bat hits a ball. Therefore, the bat body can deform in a range which allows elastic deformation without causing plastic deformation. Then, the force of restoring the outer shell wall of the bat body from its elastically deformed state (force by spring reaction) can improve the rebound force against a ball. In other words, the bat disclosed in U.S. Pat. No. 5,415,398 satisfies the both demands of improving the rebound characteristics for hitting a ball farther and securing a sufficient strength of a bat by combining the thin outer shell wall of the bat body and the insert placed to leave a gap between the insert and the outer shell.
Further, grease which is sealed in the gap enables smooth transfer of impact force, which is caused when the bat hits a ball, from the outer shell wall of the bat body to the tubular insert. As a result, the rebound characteristics of the bat can be improved further.
As described above, the bat disclosed in U.S. Pat. No. 5,415,398 has superior rebound characteristics and can increase the hit distance of a ball.
However, the bat disclosed in U.S. Pat. No. 5,415,398 requires formation of a minute gap between the bat body and the tubular insert at a high dimensional accuracy in order to realize the above described superior rebound characteristics. To implement good rebound characteristics at the entire circumference of the bat, it is also necessary to strictly control and set the height of the gap between the bat body and the tubular insert so as to be uniform at the entire circumference of the bat. Accurate formation of such a minute gap in the bat manufacturing process takes a lot of trouble and time, which results in the increased bat manufacturing cost.
Although above described U.S. Pat. No. 5,415,398 discloses a bat which contains grease sealed in the gap, the grease in this case has to be relatively high in viscosity because a failure such as leakage of the grease from the gap to the outside of the bat in use should be prevented. Since the process of sealing such viscous grease inside the gap also takes a lot of trouble and time, the bat manufacturing cost is further increased.
One object of the present invention is to provide a baseball or softball bat capable of increasing the hit distance of a ball and reducing the manufacturing cost.
Another object of the present invention is to provide a method of manufacturing a baseball or softball bat capable of increasing the hit distance of a ball and reducing the manufacturing cost.
According to one aspect of the present invention, a baseball or softball bat including a hitting portion, a taper portion, and a grip portion includes a tubular member and a metal tubular member. The tubular member includes an outer circumference plane extending from the hitting portion to the grip portion, and an inner circumference plane located inside the outer circumference plane and extending from the hitting portion to the grip portion. The metal tubular member is placed between the outer circumference plane and the inner circumference plane at least in the hitting portion The metal tubular member has a weak boundary layer formed on its surface.
Since the metal tubular member is placed between the outer circumference plane and the inner circumference plane of the tubular member is described above, the metal tubular member can improve the strength and durability of the bat. That is, the tubular member can be made thinner while the bat strength is maintained as compared with a case where the metal tubular member is not placed. Further, by forming the weak boundary layer, the tubular member and the metal tubular member can deform independently from each other when the bat hits a ball. Therefore, as compared with a case where the tubular member and the metal tubular member are bonded at nearly the entire contact plane, a portion of the tubular member which is located on the outer circumference side of the metal tubular member can elastically deform easily when the bat hits a ball. The force of restoring the portion of the tubular member from the elastically deformed state can increase further the hit distance of a ball. It is noted that the weak boundary layer is a layer which exists on the surface of a body to be bonded (the surface of the metal tubular member) and does not have the mechanical strength higher than a targeted bond strength. The weak boundary layers are, for example, grease which covers a metal surface and a lubricant for a molded plastic surface. In a region where the weak boundary layer is formed, the metal tubular member and the tubular member contact with each other without being bonded.
If the weak boundary layer is formed on the surface of the metal tubular member in this manner, the effects as described above similar to a case where a tubular insert is placed inside the tubular member so as to leave a gap therebetween can be obtained, and the conventional complicated process of adjusting the height of the gap is unnecessary. In other words, a bat can be manufactured so that the surface of the metal tubular member and the tubular member contact with each other with the weak boundary layer therebetween. Since the bat manufacturing process can be simplified as a result, the increase in the bat manufacturing cost can be prevented.
Since the bat strength against impact when hitting a ball is prevented from being insufficient by the metal tubular member, accidents such as cracking of the bat tubular member and breaking of the bat due to impact when the bat hits a ball can be prevented.
Since the metal tubular member is placed between the outer circumference plane and the inner circumference plane of the tubular member, the bat according to the present invention can have a structure in which the metal tubular member is buried in the tubular member. According to such a structure, the position of the metal tubular member can be fixed without bonding the surface of the metal tubular member and the tubular member with adhesive, for example (while a weak boundary layer is formed on the surface of the metal tubular member).
In the baseball or softball bat according to the one aspect, the tubular member may include a first layer located on the outer circumference side of the metal tubular member and a second layer located on the inner circumference side of the metal tubular member.
In this case, the first and second layers can be formed of different materials from each other. Therefore, a material which is elastically deformed easily by impact force when a bat hits a ball is used for the first layer to improve further the rebound characteristics of the bat, a material which is higher in rigidity than the first layer is used for the second layer, and thus the bat strength and durability can be improved. As a result, the accident of a broken bat, for example, can be prevented while increasing the rebound characteristics of the bat.
In the baseball or softball bat according to the one aspect, the weak boundary layer may include a layer which is formed by providing non-adhesive surface treatment on the surface of the metal tubular member.
In this case, the bond between the surface of the metal tubular member on which the weak boundary layer is formed and the tubular member can be reliably prevented.
In the baseball or softball bat according to the one aspect, the weak boundary layer may include at least one selected from the group of a layer with a mirror surface finished upper surface, a plated layer, a lubricant coated layer, and an oxide film coated layer.
In the baseball or softball bat according to the one aspect, the weak boundary layer may be formed on one of the outer and inner circumference planes or on both the outer and inner circumference planes of the metal tubular member.
When the weak boundary layer is formed on both the outer and inner circumference planes of the metal tubular member as described above, the three parts of the metal tubular member, a portion of the tubular member which is located on the outer circumference side of the metal tubular member, and a portion of the tubular member which is located on the inner circumference side of the metal tubular member can elastically deform independently from one another when the bat hits a ball. Therefore, the hit distance of a ball can be increased further by transfering to the hit ball the force of restoring the three parts from the elastically deformed state.
When the weak boundary layer is formed only on the outer circumference plane of the metal tubular member, a portion of the tubular member which is located on the inner circumference plane side of the metal tubular member can function as a reinforcing member for increasing the strength of the metal tubular member. As a result, the bat strength can be increased further.
In the baseball or softball bat according to the one aspect, the tubular member may include a fiber reinforced plastic (FRP).
In the baseball or softball bat according to the one aspect, the tubular member may be formed by impregnating a resin into a fiber member which is formed to a tubular shape.
According to another aspect of the present invention, a method of manufacturing a baseball or softball bat including a hitting portion, a taper portion, and a grip portion includes the steps of forming a tubular inner circumference layer to extend from the hitting portion to the grip portion, placing a metal tubular member at least on a region of the inner circumference layer which is to be the hitting portion, forming a weak boundary layer on the surface of the metal tubular member, and forming a tubular outer circumference layer to cover at least the metal tubular member.
By thus placing the metal tubular member on the inner circumference layer and forming the outer circumference layer on the metal tubular member, the baseball or softball bat according to the one aspect can be manufactured easily.
Unlike the conventional bat manufacturing method, a step of forming a gap between the metal tubular member and the inner circumference layer or the outer circumference layer is not performed, and therefore complication of the manufacturing process can be prevented. As a result, the bat manufacturing cost can be reduced.
In the method of manufacturing a baseball or softball bat according to the another aspect, the step of foing the weak boundary layer may include the step of providing non-adhesive surface treatment on the surface of the metal tubular member.
In this case, the weak boundary layer can be formed easily on the surface of the metal tubular member.
In the method of baseball or softball bat according to the another aspect, the non-adhesive surface treatment may include at least one selected from the group of mirror surface finish, plating finish, lubricant coating, and oxide film coating.
In the method of manufacturing a baseball or softball bat according to the another aspect, the step of forming the inner circumference layer may include the step of forming a tubular inner circumference fiber layer to extend from the hitting portion to the grip portion, and the step of forming the outer circumference layer may include the step of forming an tubular outer circumference fiber layer to cover at least the metal tubular member. Further, the step of impregnating a resin into the inner circumference fiber layer and the outer circumference fiber layer may be included.
In the method of manufacturing a baseball ox softball bat according to the another aspect, the step of applying pressure an the inner circumference layer toward the outer circumference layer may be further included.
In the method of manufacturing a baseball or softball bat according to the another aspect, the inner and outer circumference layers may include fiber reinforced plastic.
In the method of manufacturing a baseball or softball bat according to the another aspect, carbon fiber, glass fiber, aramid fiber, or other reinforcing fibers can be used for the reinforcing fiber member for the fiber reinforced plastic, the inner circumference fiber layer, or the outer circumference fiber layer. As the orientation anne of these reinforcing fiber, a combination of 0xc2x0 to 45xc2x0 or 0xc2x0 to 90xc2x0 with respect to the longitudinal direction of the bat is possible. The type and orientation angle combination of the reinforcing fibers are determined by the strength and other properties required for the bat.
In the method of manufacturing a baseball or softball bat according to the another aspect, a thermosetting synthetic resin such as an epoxy resin or a thermoplastic synthetic resin such as a polyurethane resin may be used as the matrix resin of fiber reinforced plastic.
According to still another aspect of the present invention, a fiber reinforced plastic (FRP) baseball or softball bat including a hitting portion, a taper portion, and a glip portion is characterized in that a metal tubular member having a weak boundary layer (WBL) is buried and integrated in the interior of the fiber reinforced plastic layer (FRP layer) which corresponds to the hitting portion.
Therefore, the FRP layer can be made thinner while the necessary strength as the FRP bat is maintained. Further, by thus burying the metal tubular member having the weak boundary layer inside the FRP layer, a non-adhesive interface dissociation layer can be formed at the boundary plane of the surface of the metal tubular member on which the weak boundary layer is formed and the matrix resin layer of the FRP layer. On the non-adhesive interface dissociation layer, a physical phenomenon in a springback manner is instantaneously caused between the metal tubular member and the FRP layer when the bat hits a ball. As a result, the springback physical phenomenon can improve the rebound characteristics of the bat.
Since the FRP layer exists even on the inner circumference side of the metal tubular member, plastic deformation of the metal tubular member itself due to impact force when the bat hits a ball can be prevented effectively. As a result, the durability of the bat can be improved.
In the baseball or softball bat according to the still another aspect, the metal tubular member may be buried and integrated between the FRP outer and inner shell layers of the fiber reinforced plastic layer.
In this case, the metal tubular member is completely buried and integrated in the FRP layer, and therefore the FRP outer shell layer can be made thinner while the strength required as the FRP bat is maintained. As a result, the rebound characteristics of the bat can be improved, which in turn can improve the hit distance of a ball.
Since the FRP inner shell layer exists on the inner circumference side of the metal tubular member, the FRP inner shell layer can function as a reinforcing member for the metal tubular member. As a result, the durability of the PRP bat can be improved reliably.
In the baseball or softball bat according to the still another aspect, the weak boundary layer may be a region in which mirror surface finish, plating finish, lubricant coating, oxide film coating, or other physical or chemical non-adhesive surface treatment is applied on the surface of the metal tubular member. Further, the weak boundary layer may be formed on one of the outer and inner circumference sides or on both the outer and inner circumference sides of the metal tubular member.
As described above, in the baseball or softball bat according to the still another aspect, the bat hitting portion is the three-layer structure of two thin FRP layers and one layer of the metal tubular member. There is not any gap provided between the layers When the FRP layers and the layer of the metal tubular member are completely adhered, the above described three layers integrally deform when the bat hits a ball. Thus, they virtually deform just as one thick FRP layer. Since the elastic deformation amount of the FRP layer is very small in this case, the effect of increasing the hit distance of a ball by utilizing the force of restoring the layers from the elastically deformed state is relatively small.
In the bat according to the present invention, however, adhesion of the FRP layers and the metal tubular member, for example, of an aluminum alloy pipe is prevented by formation of the weak boundary layer. Therefore, the FRP layers and the metal tubular member can move independently from one another. Thus, the rigidity of the bat in the direction of deformation is made extremely small. As a result, the rebound characteristics of the bat when hitting a ball can be improved remarkably, and therefore the hit distance of a ball can be increased.
Unlike the conventional bat disclosed in U.S. Pat. No. 5,415,398, the bat according to the present invention does not require strict control and adjustment of the size of a gap between the metal tubular member (pipe-shaped insert) and the bat body in the manufacturing process, and the step of sealing grease in the gap. For the bat according to the present invention, therefore, the manufacturing process can be simplified. Further, the problem of fluctuated rebound characteristics of a bat caused by fluctuated gap size does not occur for the bat according to the present invention.
As described above, in the bat according to the present invention, the reliable quality can be secured, the manufacturing cost can be reduced at the same time, and the hit distance of a ball can be increased.
In the baseball or softball bat according to the one or still another aspect, carbon fiber, glass fiber, aramid fiber, or other reinforcing fibers can be used for the reinforcing fiber member for the FRP or the fiber member. As the orientation angle of these reinforcing fibers, a combination of 0xc2x0 to 45xc2x0 or 0xc2x0 to 90xc2x0 with respect to the longitudinal direction of the bat is possible. Further, the type and the orientation angle combination of the reinforcing fibers are determined by the strength and other properties required for the bat.
In the baseball or softball bat according to the one or still another aspect, a thermosetting synthetic resin such as an epoxy resin or a thermoplastic resin such as a polyurethane resin can be used as the matrix resin of FRP.
In the method of manufacturing a baseball or softball bat according to the another aspect, the reaction injection molding (RIM) process and the resin transfer (RTM) process can be used. In this case, by sucking and exhausting a mold, in which the external Shape of the bat is prepared, from the bat top end or the grip end and simultaneously introducing a matrix resin into the mold from the grip end or the top end, which are located opposite from the sucked and exhausted portion, a uniform matrix resin without air bubbles can be introduced into the mold. As a result, a high quality bat which does not include defects such as air bubbles in the matrix resin can be obtained.
In the baseball or softball bat according to the one or still another aspect, or in the method of manufacturing a baseball or softball bat according to the another aspect, an aluminum alloy pipe may be used as the metal tubular member.
In the baseball or softball bat according to the one or still another aspect, or in the method of manufacturing a baseball or softball bat according to the another aspect, 6000 type or 7000 type aluminum alloys according to the ASTM standard can be used as a material for forming the metal tubular member. Of the aluminum alloys, 7001, 7049, 7060, 7075, 7178, 6061 which particularly satisfy the ASTM standard are preferably employed. By using such aluminum alloys, the strength and durability of a bat can be improved further.
In the baseball or softball bat according to the one or still another aspect, or in the method of manufacturing a baseball or softball bat according to the another aspect, an titanium alloy or pure titanium can be used as a material for forming the metal tubular member. For example, xcex2 type or xcex1+xcex2 it type titanium alloys are preferably used.
As other materials for forming the metal tubular member, other titanium alloys (sudh as Ti-6Al-4V, Ti-4Al-22V, Ti-15V-3Cr-3Al-3Sn, Ti-4.5Al-3V-2Fe-2Mo, Ti-10V-2Fe-3Al) can be used.